1. Field of the Invention
The present invention relates generally to the field of wireless communications, and particularly to multi-band antennas used in wireless communications.
2. Background
Certain applications such as the Global System for Mobile Communications (GSM) and Personal Communications Service (PCS) require that multiple bands be accessible, depending upon the local frequency coverage available from a service provider. Because applications such as GSM and PCS are used in the context of wireless communications devices that have relatively small form-factors, a low profile is also required.
A magnetic dipole antenna (MDA) is a loop antenna that radiates electromagnetic waves in response to current circulating through the loop. The antenna element of an MDA is designed so that it resonates at the frequency required by the ultimate application for which the antenna is intended. The antenna""s resonant frequency is dependent on the capacitive and inductive properties of the antenna elements, which in turn are controlled by various dimensions of the antenna elements.
For some applications, it is desirable to expand the frequency range of an antenna to cover a wider band of frequencies. However, size constraints often make it difficult to design an antenna with a frequency band wide enough to meet these applications needs. The present invention addresses the requirements of certain wireless communications applications by providing configurations for tow profile, multi-frequency, multi-band, magnetic dipole antennas.
The present invention discloses a myriad of physical arrangements of antenna elements configured to cover one to n number of frequencies or bands of frequencies. In the present invention, the antenna elements include both inductive and capacitive parts. Each element provides frequencies or bands of frequencies. The physical design of each element can vary, but always allows for multi-frequencies by using a plurality of antenna elements to produce a multi-frequency antenna. Furthermore, the arrangement of a plurality of antenna elements allows the frequency coverage of the antenna to be enlarged.
Each antenna element is cut, folded, and/or arranged to meet both the frequency and space requirements of the specific application. In one embodiment, each antenna element comprises three arms arranged to produce multiple frequency bands. Multiple elements of relatively the same size can be arranged in various fashions such that the frequency bands produced by each element combine to enlarge each frequency band produced by each element. Alternatively, the multiple elements can be of varying sizes to increase the number of frequency bands produced by the antenna.
The ground and feed points of the antenna can be arranged in various fashions to meet the needs of a specific antenna application. In addition, filters can be added to or incorporated into the antenna elements in a variety of ways for frequency matching or to reject unused frequency bands. For example, in one embodiment the filter is formed by attaching a matching element, which can be a piece of conductive material, to the antenna element. In another embodiment, the filter can be formed by removing material from the antenna element.